Identifying the Best Flow Setting Strategy for High-Flow Nasal Cannula

The goal of this randomized trial is to compare four different flow-setting approaches for post-extubation use of high-flow nasal cannula (HFNC). Selecting the appropriate flow rate when initiating HFNC oxygen therapy is both crucial and challenging for clinicians, as the physiological benefits of HFNC depend significantly on the flow rate. To date, there are no guidelines or consensus on flow-rate setting and weaning for HFNC oxygen therapy. The investigators hypothesized that physiological marker-guided flow setting using peak tidal inspiratory flow (PTIF) or PaO₂/FiO₂ ratios lead to better extubation outcomes as compared to empirical flow setting of 40 L/min or 60 L/min. Participants will be randomly assigned to one of four study groups with different flow setting strategies summarized as follows: (1) Setting flow at 40 L/min, (2) Setting flow at 5 L/min above the peak tidal inspiratory flow, up to a maximum of 60 L/min. (3) Setting flow according to P/F ratio prior to extubation. Flow will be set at 60, 50 40 L/min if P/F ratio \<250 mmHg, 250-300 mmHg and \>300 mmHg, respectively. (4) Setting flow at 60 L/min.